MENTAL DEFICIENCY. Mental defectiveness, as de fined by the British Mental Deficiency act 1927 is, "a condition of arrested or incomplete development of mind existing before the age of eighteen years, whether arising from inherent causes or induced by disease or injury." Mental deficiency, which is often inherited as a Mendelian recessive (see HEREDITY, MENDELISM), is to be distinguished from ordinary insanity (q.v.), in which there is a definite abnormality of the mind, whereas mental deficiency is due to arrested development of an otherwise normal mind, sometimes owing to deficiency of the secretion of the thy roid gland (see HORMONE, ENDOCRINOLOGY). Legislation both in England and elsewhere has recognized the essential difference between mental deficiency and lunacy and the class of so-called "mental defectives" is generally dealt with by laws differing from those affecting the insane. These laws are based mainly on a recognition of (a) the educational, (b) the social and racial problem created by the presence of uncontrolled mentally defec tive persons in the community.
The Elementary Education (Defective and Epileptic Children) act 1899, gave to local education authorities power to provide special schools (day or residential) for mentally defective children between the ages of 7 and 16 who, not being either dull or back ward or idiots or imbeciles, were capable of benefiting by the edu cation provided in such schools. Under the Elementary Education (Defective and Epileptic Children) act of 1914 these powers were made compulsory, and both acts were embodied in Part V., sections 51-9 of the Elementary Education act 1921. Attendance at such schools may be enforced by a magistrate, provided it is clearly for the child's benefit that he should attend a special school. Owing to the War and to the relatively high cost of these schools many authorities have failed to provide sufficient, in some cases, any special schools; there is practically no school provision for defec tive children in rural areas. The estimated number of defective children is calculated at eight to ten per thousand of the school population. The latter figure is probably the more accurate. This gives an estimated total of from 42,000 to 52,000 (approximately) defective children to be provided for, but provision has only been made for 16,292 children in 170 day and 20 residential schools.
In addition, the local education authorities must notify the local control authority of children who are incapable of benefiting from education in special schools or who need to be placed under supervision or guardianship or given institutional care on leaving school. There are 109 occupation day centres, mainly in urban areas, for children excluded from schools, run for the most part by local voluntary mental welfare associations ; after-care committees and the above associations look after the children who have left special schools, try to find them employment, supervise them at home and establish handicraft centres for them.
The Mental Deficiency Acts.—The Board of Control, a section of the Ministry of Health, administers the Lunacy and the Mental Deficiency acts. The local control authorities are statutory mental deficiency committees of county and county borough councils whose duty it is to provide for defectives, only when they can be certified as idiots, imbeciles, feebleminded or moral defectives, ' and who in addition are either (a) neglected, without visible means of support, cruelly used, etc. ; (b) found guilty of any criminal offence and liable to be sent to or actually sent to an industrial school or prison; (c) notified by the local education authorities as ineducable or as needing institutional care on leaving a special school; (d) having given birth to or being pregnant of an illegiti mate child whilst in receipt of poor relief. The duty of the authority is (a) to ascertain the defectives they must deal with (b) provide by visiting and watching over the defec tive at home. This supervision is carried out either by specially appointed officers or by voluntary associations to whom statutory duties are delegated by the local authority. If this supervision is insufficient the authority may (c) send defectives to a certified institution under orders or (d) place them under guardianship under orders, i.e., under the charge of an individual having the powers of a parent over them. This order is made by a magistrate on a petition supported by two medical certificates. Orders are renewable by visiting justices at the end of each of the first two years, then every five years. The authorities must also provide suitable training or occupation for defectives who are under super vision or guardianship, or have been sent to an institution.